August 15, 2005

Study: Pain Neurons Respond to Garlic

WASHINGTON -- People tend to love garlic or hate it, but few probably associate it with pain. Nonetheless, it turns out that pain-sensing nerves respond to the sulfur-based chemicals in garlic.

Indeed, the same mechanism the body uses to react to the sharpness of chili peppers and hot mustards like wasabi is the one that detects garlic, according to a study in Tuesday's Proceedings of the National Academy of Sciences.

David Julius of the department of cellular and molecular pharmacology at the University of California, San Francisco, said the finding was made during research on the mechanisms of pain sensation.

Julius discovered that when a subset of pain neurons in rats activates a cell membrane channel called TRPA1 the result is a release of brain chemicals that stimulate blood vessel dilation and inflammation.

Understanding how such nerves work, he said, can help researchers learn more about how arthritis and some muscular problems develop.

"You can use these natural products as very interesting pharmacological probes of the pain pathways," Julius explained.

Susan Travers of Ohio State University said the most interesting finding of the paper is that the neurons that respond to garlic compounds are only a subset of those that respond to the capsaicin in hot peppers.

This type of specificity would give some basis for why people can tell the compounds apart, said Travers, who was not part of Julius' research team.

Garlic, sometimes called the stinking rose, belongs to the group of plants called allium, which also includes onions, leeks, chives and shallots. All of them produce sulfur-based compounds that make them pungent. One, called allicin, actives the set of pain sensors and is especially prominent in garlic.

In addition to its culinary properties, garlic has a long history of use in folk medicine, having been used to treat such ailments as high blood pressure, high cholesterol and even blood clots.

Capsaicin, the chemical that gives hot peppers their heat, is currently a major ingredient in a cream used by arthritis sufferers.

This and similar studies "clearly do not explain the complex sensory experience that this ingredient lends to food. It seems likely that garlic also stimulates olfactory receptors, and the olfactory system is probably largely responsible for garlic's distinctive aroma, and yet other compounds stimulate specific receptors in taste buds," Travers said.

Many cooks know that roasted garlic produces a much milder taste that the raw bulbs and Travers noted that a separate study had found that baking garlic eliminated its ability to stimulate the TRPA1 channels.